C. Venkatesh

Wavelet transform based harmonic analysis and real power measurement

This paper proposes a method of harmonics detection and theoretical basis for the measurement of reactive and distortion powers using wavelet multi-resolution technique. The proposed method decomposes the voltage/current waveforms into the uniform frequency bands corresponding to the odd-harmonic components of the signal and uses a method to reduce the spectral leakage due to the imperfect frequency response of the used wavelet filter bank. The harmonic analysis has been performed on typical distribution system and compares the performance of the proposed method with the results obtained using the discrete Fourier transform (DFT) analysis. The measurement of real power relies on the use of broad-band phase-shift networks to create concurrent in-phase currents and quadrature voltages. The advantage of viewing the real and reactive powers in the wavelet domain is that the domain preserves both the frequency and time relationship of these powers. The harmonic analysis and real power measurement in a typical distribution system using wavelet multi-resolution technique is verified in MATLAB/SIMULINK environment.

Classification of voltage sag, swell and harmonics using S-transform based modular neural network

This paper presents classification and characterization of typical voltage disturbances- sag, swell, interruption and harmonics employing S-transform analysis combined with modular neural network. S-transform is used to extract various features of disturbance signal as it has excellent time-frequency resolution characteristics and ability to detect disturbance correctly even in the presence of noise. Classification is performed using modular neural network with features extracted from S-transform. Modular neural network is designed by modifying the structure of traditional multilayer network into modules for each disturbance to provide less training period and better classification. Disturbances are characterized by magnitude and phase information using S-transform analysis. Simulation and experimental results show that S-transform combined with Modular neural network can effectively detect, classify and characterize the disturbances.

Detection of voltage sag/swell and harmonics using discrete S-transform

This paper shows the application of S-transform in identifying the voltage disturbances such as sag, interruption, swell and harmonics. S-transform is suitable for the analysis of power quality disturbances under noisy condition as it has excellent time-frequency resolution characteristics and has the ability to detect the disturbance correctly. Various voltage disturbances are generated as per IEEE Std. 1159 using MATLAB. S-transform analysis performed on these disturbance signals can identify the magnitude and duration of the disturbances. The effectiveness of the S-transform is shown for multiple sag/swell condition in the presence of transients or noise. Wavelet transform is also used for analysis and results are compared. Simulation results are also shown to identify both the harmonic magnitudes as well as their phase using S-transform analysis. Experimental verification has been performed with transmission line model connected to linear and non-linear loads and S-transform is used to detect and classify various voltage disturbances.

Mitigation of Voltage Sag/Swell Using Peak Detector Based Pulse Width Modulation Switched Autotransformer

Abstract This article presents the fast detection of voltage sag/swell events by employing peak estimation of the signal. The algorithm used is very fast compared to event detection using root mean square calculation. A mitigation device with a pulse width modulation controlled autotransformer is employed for compensation of voltage sags/swells in a distribution system. This device does not require any energy storage device unlike mitigation devices employing DC-to-AC converter topology. Simulation results for mitigation of voltage sag due to faults/induction motor start and voltage swell due to capacitor switching show that nominal load voltage is achieved with a pulse width modulation switched autotransformer employing the peak estimation technique. The transient response of the device is about one cycle, and the total harmonic distortion of the load voltage is found to be within limits. A prototype model of a 230-V 2.5-kVA pulse width modulation switched autotransformer device is tested for mitigation of voltage sag/swell in an artificial transmission line system, and experimental results show that the device performance is satisfactory.

S-transform-based Hybrid Active Filter for Mitigation of Current Harmonics

Abstract This article presents a new control strategy for the hybrid active filter using S-transform. Frequency-domain analysis employing S-transform is used to extract the fundamental component of the non-linear load current. The switching patterns for the active filter are generated with pulse-width modulation. The proposed technique is simple and has better performance, even with low switching frequency, as compared to time-domain techniques. Simulation results are presented for steady-state and transient conditions, and the hybrid active filter is effective in maintaining the source current harmonics within the limits.

Mitigation of voltage sags/swells using PWM switched autotransformer

Dynamic voltage restorer and STATCOM are normally employed as a solution for mitigation of voltage sag and swell. This paper presents modelling and analysis of PWM switched autotransformer as a mitigating device for voltage sag and swell disturbances. The proposed system has less number of switching devices and has good compensating capability in comparison to commonly used compensators. Simulation analysis of three-phase compensator is performed in PSCAD/EMTDC and performance analysis of the system is presented for various levels of sag and swell. The THD of the load voltage when the compensator is functioning during disturbance condition are within the limits. Also the compensator can maintain the load real and reactive powers constant. Simulation results are presented for various conditions of sag and swell disturbances in the supply voltage to show the compensation effectiveness.

Estimation and mitigation of voltage and current harmonics in distribution systems

The widespread application of power electronics is introducing non-linear loads in the distribution system resulting in the distortion of current and voltage waveforms. In this paper, IEEE 13-bus distribution system is considered for analysis of harmonics. The distribution system model is simulated in PSCAD/EMTDC software with static and adjustable speed drives as loads. Harmonic analysis of the system gives the harmonic spectrum and THD of currents and voltages at various buses. Mitigation of harmonics is performed by simulation using single tuned, double tuned, reactance one-port filters. Comparative analysis of filter performance is presented. The simulation study show that the best performance of the filter is obtained when positioned at/near the nonlinear load buses.

Wavelet feature-based modular neural network for detection and classification of power quality disturbances

Disturbances such as voltage sag, swell, interruption and harmonics are very typical in a power system. Power quality monitoring should be capable of identifying these disturbances to initiate mitigation action and protect sensitive loads. This paper presents wavelet-neural network-based detection and classification of power quality disturbances. Wavelet transform has the ability to analyse signals simultaneously in both time and frequency domains and is used to extract features of the disturbances by decomposing the signal using multi resolution analysis. These features, used to detect and localise the disturbances and are not easily separable, will reduce the performance of multilayer neural network. Improvement in the classification accuracy is suggested by employing modular neural network obtained by dividing a complex task into easier subtasks. The algorithm proposed is tested for classification of various power quality disturbances and it is found that a modular neural network has a higher classification accuracy over traditional multilayer neural network.

Detection of transmission line faults in the presence of STATCOM using wavelets

In this paper, wavelet transform technique is applied to detect fault in the transmission line with flexible alternating current transmission (FACTS) device. Presence of FACTS device changes the system impedance and hence makes it difficult to detect faults on the line which may result into maloperation of relay. Three phase currents are monitored at both ends of the transmission line using global positioning system synchronizing clock. Wavelet transforms, which is very fast and sensitive to high frequency signal is used to extract transients in these line currents for fault detection. Fault index is calculated based on the sum of local and remote end detail coefficients and compared with threshold value to detect the fault. Proposed technique is tested for various faults and fault inception angles with and without static synchronous compensator (STATCOM) device. Simulation results are presented showing the selection of proper threshold value for fault detection.

Mitigation of voltage sag using time-ratio-controlled autotransformer

This paper presents analysis of time-ratio-controlled autotransformer as a mitigating device for voltage sag disturbance. Control circuit based on load RMS and voltage sag sensing circuit based on peak detection are employed. Commonly dynamic voltage restorer and STATCOM are employed for mitigation of voltage sag. The proposed system has less number of switching devices in comparison to commonly used compensators. Simulation analysis performed in PSCAD/EMTDC for three-phase compensator and performance analysis of the system is presented for various percentages of sag. The THDs of the load voltage and current when the compensator is functioning during disturbance condition are within the limits. Also the compensator can maintain the load reactive power constant. Simulation analysis is performed for various sag conditions like constant voltage sag due to faults and variable voltage sag due to induction motor starting. Simulation results are presented to show the effectiveness of the mitigating device in compensating voltage sag.